The present invention relates to an adhesion promotor or, more particularly, to an adhesion promotor having an activity to improve the adhesive bonding of various types of sealants, liquid silicone rubbers and the like to the substrate surface, of which the stability during storage is greatly improved.
As is well known, various types of polymeric sealants are widely used for the purpose of adhesive bonding of electric and electronic parts, sealing or caulking of interstices in building construction works and the like including polyurethane-based and silicone-based ones. A problem in the use of these polymeric sealants is the relatively low adhesive bonding strength thereof to the surface of a substrate made of a metal or plastic resin so that it is a conventional practice that the substrate surface to be adhesively bonded with a sealant is treated in advance with an adhesion promotor or a so-called primer or the sealant is admixed with a small amount of such an adhesion promotor before use.
Several types of adhesion promotors are known in the prior art of which a reaction product of an aminosilane and an epoxysilane is effective according to the disclosure in Japanese Patent Publications Nos. 52-8854 and 55-41702 although an adhesion promotor of this type is defective due to the low stability thereof during storage after preparation to cause eventual gelation or loss of the adhesion-promoting activity within only a few days even at room temperature. The reason for the low stability is presumably the substitution reaction of the alcoholic hydroxy groups produced by the reaction between the amino groups and the epoxy groups for the alkoxy groups of the alkoxysilane as an ingredient of the silicone-based sealant composition to form an inactive cyclic structure or to increase the molecular weight of the silicone component. No effective means, however, has been proposed to solve this problem.